Hooking two in series should work but you will have differences due to battery chemistry from age, differing bettery types, etc that will probably result in one being slightly overcharged while the other is slightly under.

The voltage from the high battery will continually try to charge the low battery. The voltage read from a VOM will be an average of the two batteries. You'll be doing what the solar power people call an equalizing charge. You'll be forcing power in until all batteries are brought up to the level of the highest battery or the charger cutoff voltage whichever is lower. Might cook a weak battery. If both batteries are in good condition, probably work. Make sure they are the same chemistry, either liquid, AGM, etc.

buster6315 wrote on 11/04/17 at 09:36:28:


Series = double voltage
Parallel = double amperage


Unless you have a 24 volt charger, don't do series!

Best is to simply get a "Battery Tender" Which is designed to charge a moderately down battery, and then maintain the charge.  Great for extended NON-use of the motorcycle such as a month or so of storage or through the non-riding winter season.

buster6315 wrote on 11/04/17 at 03:28:26:


Most modern battery chargers that include a digital dispaly are "smart" and will turn themselves off when the battery reaches a full charge.  The problem with them is that for some reason they also see a dead battery the same as a fully charged one - so they won't turn on if the battery is completely dead......so the old chargers are needed for a fully dead battery......or you can connect a good battery in parallel with the one that needs to be charged to fool the smart charger.

If your charger goes into a "float" mode....it sounds like your charger will recognize a charged battery and function to maintain the battery. Does the manual claim it can be used as a "maintainer"?  I don't know if chargers and maintainers both shut off at the same voltage....the charger could be shutting off at a higher voltage than a maintainer.

If you already have battery tenders and want to use a cheap non regulated one then wouldn't the old fashioned method work well where you estimate the charge from the voltage and just give it as many Ah's as you reckon it needs.

For example if you have a 12Ah batter and it's a wet cell and is reading 12.4V you might estimate it to be at 50% charge so if you have a 1.2A charger putting out 14V give the battery 6 hours at 1.2A which should give you that final 50% plus a bit extra lost due to heat.


buster6315 wrote on 11/05/17 at 04:51:29:


As someone once said "I can't afford cheap shoes"

I have battery maintainers on several vehicles I don't use in winter, sometimes for as long as five months, and I have been doing that for several years. I have not fried a battery yet.

Kris01 wrote on 11/07/17 at 17:28:38:

The bikes are in storage and the batteries are on chargers in the (ventilated) basement. It's a little inconvenient, and I might forget, but I think I may try that.
By the way, I notice that the AGM battery from my Honda CB360 charges much more quickly than the flooded battery from my S40, and they are about the same age with similar output ratings. I wonder if that means anything?